The present invention relates to a honeycomb structure. More particularly, the present invention relates to a honeycomb structure which can be suitably used, for example, as a catalyst carrier in the catalytic converter for exhaust gas purification, of internal combustion engine (e.g. automobile engine).
Honeycomb structures are in wide use in filters, catalyst carriers, etc. and are being used in large amounts particularly as a catalyst carrier in the catalytic converter for exhaust gas purification, of internal combustion engine (e.g. automobile engine), a filter for exhaust gas purification, of diesel engine, etc.
In such applications, the honeycomb structure is used by being held in a can or the like via a holding material, in some cases. In such cases, the honeycomb structure need be held at a given strength in order to avoid the slip between the can and the honeycomb structure which may occur during the actual use of the canned honeycomb structure, and the honeycomb structure is required to have an isostatic strength to withstand such holding. In such applications, the honeycomb structure is further required to have thermal shock resistance because the honeycomb structure is subjected to frequent heating and cooling.
In consideration of increasing environmental problems, the regulation for exhaust gases is becoming increasingly stricter. To respond thereto, the catalyst for exhaust gas purification made of a honeycomb structure catalyst carrier, used in the catalytic converter for exhaust gas purification, of automobile or the like needs to have higher purification ability. On the other hand, in engine development, lower fuel consumption and higher output are being aimed clearly; in respond to such movement, the catalyst for exhaust gas purification is also required to give a lower pressure loss.
Hence, in order to satisfy such requirements, such a movement is becoming increasingly strong that the honeycomb structure is allowed to have even smaller thicknesses in the partition walls and the outer wall so that the gas flow therethrough becomes easier, the pressure loss thereof becomes lower, and further the exhaust gas purification catalyst made thereof becomes lighter for smaller heat capacity and increased purification ability during engine warm-up.
In order to solve the problem of the reduction in strength of honeycomb structure, associated with the thinning of partition walls, there was proposed a honeycomb structure in which the thicknesses of partition walls are made smaller regularly toward the center of the cross-section (for example, JP-B-1979-110189). There was also proposed a honeycomb structure in which the partition wall thicknesses of peripheral portion are made larger than those of interior portion (for example, JP-A-1979-150406 and JP-A-1980-147154). There was further proposed a ceramic-made honeycomb structure in which, in order to inhibit from chipping of edge during handling, the average thickness of partition walls is set at 0.05 to 0.13 mm, the average thickness of outer wall is made larger than the average thickness of partition walls, and the relation between partition wall and the average contact width W of outer wall is W>T and 0.7≧W≧−(T/4)+0.18 (for example, WO 98/05602). There was also disclosed a honeycomb structure in which each cell is a hexagon and the outer wall is covered with a reinforcing material (for example, JP-A-1975-77291). These honeycomb structures, however, are unable to satisfy canning characteristic and thermal shock resistance at the same time.